The invention relates to a method and apparatus for controlling the driving speed of a vehicle by entering a set speed into a control unit as a driver command. In a first operating mode of the speed control device, a reference variable of the speed control unit is varied within a specified (or specifiable) speed environment (that is, a range) of the set speed, depending on an evaluation a section of road ahead of the vehicle, and on maintaining a state of the vehicle which achieves a minimum fuel usage.
Methods for controlling the driving speed of a vehicle are known. The speed control device can be designed as a master controller, in which a target value (which can be changed over time) can be provided as reference variable. The reference variable can thus be varied within the speed environment of the set speed, so that a fuel usage of the vehicle is as low as possible results.
German patent document DE 103 45 319 A1 discloses a predictive speed control for a motor vehicle, which uses information relating to the current vehicle position and also the ground ahead to save fuel and to increase traveling comfort. A vehicle operating cost function is defined on the basis of environment parameters, vehicle parameters, vehicle operating parameters and road section parameters. Vehicle control parameters are calculated and stored, which minimize the vehicle operation cost function. Current vehicle operation is controlled based on the optimized vehicle control parameters.
One object of the invention is to provide an improved speed control device for a vehicle, and especially to provide an improved operability of such a speed control device.
This and other objects and advantages are achieved by the method and apparatus according to the invention, which provides a speed control device—also known as cruise control or cruise control regulator—into which a set speed can be entered as driver command. In a first operating mode of the speed control device, a reference value entered therein is varied within a specified (or specifiable) speed environment of the set speed, based on an evaluation of a section of road ahead of the vehicle and based on maintaining a state of the vehicle with regard to achieving a fuel usage as low as possible. The method according to the invention includes the following steps: detecting a change of the set speed; changing over from the first operating mode to a second operating mode of the speed control device when the change of the set speed is detected; determining the reference variable in the second operating mode depending on the change in such a manner that the speed control device is tuned to a higher driving speed with an increase of the set speed resulting from the change, and to a lower driving speed with a decrease of the set speed resulting from the change; and changing back from the second operating mode to the first operating mode if an interruption criterion is fulfilled.
The tuning process towards the higher or lower driving speed can advantageously be perceived by the driver, who has either increased or decreased the set speed as a driver command. After the change of the set speed, the speed control device advantageously behaves for the driver of the vehicle in a tangible manner that is the same as (or similar to) a speed control device where the reference variable (in the sense of a setpoint) is always set to the set speed. Advantageously, the driver can be signaled by means of the tuning process that the speed control device has registered the new set speed, so that an optical and/or acoustic display unit for symbolizing the set speed can advantageously be dispensed with.
After the feedback to the driver by means of the tuning process, the system can advantageously change back to the usage-optimal first operating mode, in which the reference variable is varied to achieve a minimal fuel usage. For this purpose, the interruption criterion can advantageously be checked, and, if it is fulfilled, the system can change back again to the first operating mode. The speed control device can be operated in a simpler and more intuitive manner by means of the feedback, where inadvertent multiple inputs can for example be avoided due to the feedback. The reference variable can be generated by means of a suitable device with regard to minimum usage, and the speed control device in the form of a master controller.
The following steps are provided in one embodiment of the method according to the invention: determining a difference value of the change of the set speed, determining an actual value of the reference variable at the time when the change occurs, and, setting the reference variable to a sum of the actual value of the reference variable and the difference value of the change. The difference value of the change of the set speed can take on both positive and negative values, it being positive with an increase of the set speed and negative with a decrease of the set speed. The currently existing reference variable (that is, the actual value of the reference variable) can advantageously be determined. The actual value of the reference variable issued at the time of the change can advantageously be increased or decreased by exactly the amount that the driver enters by means of a change of the set speed as a driver command. The tuning process thereby advantageously takes place in the second operating mode by exactly this amount, just as the driver is used to from a conventional speed control device with a setpoint jump. The driver can thus experience the feedback in a particularly concise manner, and know that the change of the set speed was successful.
The following step is provided in another embodiment of the method: setting the reference variable to the sum of the actual value of the driving speed at the change and the difference value of the change. A control deviation can result due to a reference behavior of the speed control device or due to outside influences (e.g., wind). The driver can advantageously be provided with a tuning process as feedback, starting with the current driving speed (that is, the actual value of the driving speed). The tuning process experienced by the driver as feedback is thus more similar to the one after a constant drive (that is, a target value jump with a tuned state of the speed control device) and can thus advantageously provide an even better and more intuitive feedback of the change of the set speed.
In a further embodiment of the method, the system changes back to the first operating mode as soon as a period of the interruption criterion has elapsed. The period can advantageously be chosen in such a manner that the driver experiences a sufficient feedback regarding his change of the set speed. It is possible, for example, to choose the period such that the tuning process known to the driver as such from conventional speed control devices is predominantly finished.
In a further embodiment of the method according to the invention, the following step is provided: changing back to the first operating mode as soon as a control deviation of the interruption criterion (15) falls below a threshold. Advantageously, the extent to which the tuning process has progressed can thus be determined by means of the interruption criterion. The threshold for the control deviation can advantageously be chosen so as to ensure that the tuning process is terminated; that is, the driver has noticed it certainly also as feedback.
In a further embodiment of the method according to the invention, the following steps are provided: switching from the second operating mode to a third operating mode as soon as the interruption criterion is fulfilled; calculating a target value of the reference variable at the interruption criterion which corresponds to the first operating mode; determining the actual value of the reference variable at the interruption criterion, and bringing the reference variable from the actual value of the reference variable to the target value of the reference variable at the third operating mode; and changing from the third operating mode to the first operating mode after the approach.
A sudden change of the reference variable—which would be seen by the driver as a further tuning process in an annoying manner—can advantageously be prevented during the changeover from the second operating mode to the first operating mode. The third operating mode can advantageously be interposed until the reference variable is brought up to the target value of the reference variable. The target value of the reference variable can thereby be calculated by the corresponding device in such a manner, as if the speed control device would be in the first operating mode. Indeed, another reference variable is supplied to the speed control device, which lies between the actual value of the reference variable determined at the change and the target value of the reference variable. An approach in this context can mean a steady progress, for example a monotonously increasing or monotonously decreasing progress, which is actually the reference variable passed on to the speed control device during the third operating mode.
With a speed control device for the predictive control of the driving speed of a vehicle depending on a set speed which can be provided and on a distance profile of a section of road ahead of the vehicle, the object is further solved in that the speed control device is arranged to modify the driving speed in response to a sudden change of the set speed aligned with the change of the set speed, preferably by the same amount of change, and to regulate it temporarily to a constant speed level. The variation of the driving speed, otherwise dependent on the distance profile, is disabled temporarily by the temporary control to the constant speed level.
The distance profile of the section of road ahead of the vehicle, especially its elevation and/or the curvature profile, is determined in a predictive manner by a positioning determining system supported by satellite and a digital map.
The invention also provides a motor vehicle having a speed control device for controlling a driving speed of the vehicle. The speed control device is designed, arranged and/or constructed for carrying out a method described previously. The previously described advantages result.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.